CFD research of AP1000 hot-leg suction effect and temperature heterogeneity

The lateral flow in top core region and upper plenum is detrimental for power control. The temperature heterogeneity in hot-legs induces the deviation of estimation of power level. Therefore, to investigate the lateral flow at the core outlet and temperature heterogeneity in the hot-legs of AP1000, a CFD analysis of the domain from the core inlet to hot-leg outlet was conducted. The core region was simulated by introducing additional source term in the momentum equations instead of being reconstructed in detail. A volumetric power density of hot full power derived from AP1000 middle of life was applied to the active core zone. The main internal components including control guide tubes with eight large opening windows on it and support columns were kept, while other little components including control rod assemblies were omitted to decrease the total mesh quantity. The Reynolds-averaged Navier-Stokes equations was solved with Realizable k-ε turbulence model using commercial CFD code FLUENT. The coolant temperature map at the core outlet and the extent of the hot-leg suction effect on the top core region were obtained. Compared with the temperature field at core outlet, the maximum temperature difference at the entrance of the hot-leg drops 10K after the mixing in the upper plenum. The hotter coolant from central fuel assemblies remains at the upper part of the hot-leg, while the cooler coolant from peripheral fuel assemblies stays in the lower part of the hot-leg. The temperature heterogeneity and its evolvement along the hot-leg were analyzed.